Use of sap-flow sensors to schedule vineyard irrigation. II. Effects of post-veraison water deficits on composition of Shiraz grapes

Transpiration rates of Shiraz vines grown on a two wire vertical trellis we re measured using sap-flow sensors and used as a basis for applying differe nt levels of post-veraison irrigation. The effect of this differential irri gation on plant water status and grape composition were investigated with r esponses of vines on the upper and lower wires of the trellis studied separ ately. The concentration of juice total soluble solids and pH was unaffecte d by irrigation treatment but the concentration of berry anthocyanins and p henolics, expressed as mg/g berry mass and absorbance units/g berry mass re spectively, decreased with increase in water application, mainly due to an increase in berry weight. Predawn leaf water potential was measured from ve raison to harvest and the water stress integral (S-psi) was calculated as a n indication of the intensity and duration of water stress in the three irr igation treatments. S-psi was found to be closely correlated with post-vera ison water use and with grape composition.